Internet Protocol Multimedia Subsystem (IMS) is a standardized set of specifications that describes a Next Generation Network (NGN) with a generic architecture for Internet Protocol (IP)-based telephony and multimedia services. Third Generation Partnership Projects (3GPP/3GPP2) enable and support the evolution of mobile networks beyond second-generation (2G) mobile systems such as Global System for Mobile Communications (GSM) and radio technology initially defined IMS. IMS was also adopted by other standardization bodies (e.g., Wi-MAX and TISPAN) for their future networks. IMS uses Session Initiation Protocol (SIP) to control multimedia communication sessions such as video and voice calls over IP (VoIP). Benefits of IMS core networks include, for example, VoIP and multimedia services, as well as Instant Messaging and presence, standardized interfaces, reusable components, and improved Quality of Service (QoS) mechanisms, etc.). Telecommunication Service Providers (TSPs) are investing in and deploying IMS/IP core networks to provide these benefits to subscribers.
TSPs with a legacy mobile network typically want to take advantage of IMS Application Server provided services. However, due to limited protocol support and other limitations of device capabilities, many legacy devices today lack implementation support for IMS services. Home telephones, for example, are often stand-alone systems that communicate primarily using legacy, wired telephone infrastructures. Although wireless home telephones are widely used, they normally are not part of the more integrated infrastructure and information corpus with which our cellular phones and personal computers communicate. Such legacy devices cannot generally take advantage of IMS Operator provided services.